As adhkar are a recommendation you have the free choice.
You should only follow the recommendations of the based ahadith, for example if there's an amount of repetition you should do it as stated. Else there's no limitation nor a minimum.
As salaamu alaikum wa rahmatullahi wa barkatahu,
In the name of Allah the most benificient and merciful.
You can do dhikr and azhkar as many times as you want there is nothing bidah in doing dhikr more than 100 times in any situation neither it's been said that doing dhikr more than 100 times is bidah. Also praying nafl prayers is good and you can pray as ...